1. Field of the Invention
The present invention relates to a valve device incorporated in pipings in a factory or plant.
2. Description of the Related Art
In recent years, as regards the air pollution problem, there is much debate on the effluent control of, particularly, volatile organic substances. In the United States and Germany, regular inspection of leakage and maintenance obligation for piping equipments of industrial plants are legally controlled, and many countries and regions are expected to follow this trend.
In compliance with the regulations, it is required that the gland sealing be maintained for a long term. Needless to say, this also meets the user's requirement that the repair cycle of equipments would like to be lengthened irrespective of types of fluids.
For this reason, packing manufacturers have provided new packings with high sealing characteristics on the one hand. Equipment manufactures have provided valve devices having a live load structure (Live Load Packing System) compensating for reduction of packing tightening force on the other hand.
In general, the gland packing used for the sealing member of fluid equipment reduces the tightening force thereof and thereby deteriorates the sealing characteristic as service time goes by. The live load structure compensates for this reduction by the restoring force of a spring, and the use of the structure has conventionally been recommended.
U.S. Pat. No. 5,056,757 (hereinafter, referred to as Patent Document 1), for example, discloses a valve device in which Belleville springs are stacked between a packing follower and a packing flange in externally exposed condition as one example of the valve device using the live load structure. FIG. 10 is a longitudinal sectional view showing the valve device disclosed in Patent Document 1.
Referring to FIG. 10, Belleville springs 5 are externally exposed between a packing follower 3 and a packing flange 9, and thereby, the valve device has an advantage that the stacked pattern of the Belleville springs 5 is easily checked. This is because the load characteristic of the live load mechanism is determined by the direction of building-in the Belleville springs 5 and the number of the springs.
However, there is a possibility that dust or the like adheres to the surface of the Belleville springs 5. Because the space in the stacked portion of the Belleville springs 5 is narrow, the dust, which once adhered thereto, is not flushed even by wind and rain, and there is a possibility that the Belleville spring is corroded even if the spring is made of stainless steel.
Further, U.S. Pat. No. 5,190,264 (hereinafter, referred to as Patent Document 2), for example, discloses a valve device having a live load structure that is prevented from external dust by placing Belleville springs within its packing follower, as another example of the valve device employing the live load structure. FIG. 11 is a longitudinal sectional view showing the valve device disclosed in Patent Document 2.
Referring to FIG. 11, the packing follower 3 accommodates the Belleville springs 5. This makes the valve device have a structure in which external dust does not easily adhere thereto.
However, even in the valve device disclosed in Patent Document 2, there is a possibility that the Belleville spring is corroded even if the spring is made of stainless steel, because the rain water, which once entered the device, is not readily removed. Further, there is another problem that the stacked pattern of the Belleville springs 5 cannot be seen from outside, which rather causes inconvenience.
Because the conventional valve devices have been arranged as described above, there is a problem that dust tends to adhere to the stacked portion of the Belleville springs.
Moreover, when the valve device had a structure in which the stacked portion of the Belleville spring resists the adhesion of dust, there arises a problem that the rain water, which entered the stacked portion of the Belleville spring, is not easily removed.
Furthermore, there is another problem that, when the valve device had a structure in which the stacked portion thereof resists the adhesion of dust, the stacked pattern of the Belleville springs cannot be visually checked from outside.